I as thinking about obtaining a hardness tester to check my blades after heat treat and tempering is complete. Since I make knives more for a hobby, I don't have a big budget. I've sold only 7 knives. (Two more being made right now.) Also I have a small shop, and there isn't much room left, so I was thinking about a hand held tester.

I could use some advice on just about everything regarding these testers, I've never used one before, so simple operation would be useful.
Which are the good manufacturers?
What do I really need or do I even really need one?
Are the hand held testers any good?

Not as precise, but a whole load cheaper and easier to store. That, and lets be honest, how many of us actually need to know the exact hardness of a blade? Ballpark is good enough for me at least, im perfectly happy with oxide colors and temperature control telling me the hardness

I saw those when I did a Yahoo search on hardness testers. The set was a little less than $100. There were no instructions on use, bit I figure that you try different files until you find one that actually "bites" into the metal and that gives a general indication of hardness.

You make a valid point, which was something I was wondering about, how important is it really to know the exact RC hardness? If the blade passes various inexpensive tests (which we discussed in my D2 heat treating post in the Newbies area) is it really necessary to spend hundreds to thousands of $$$$ for a big bulky tester?

Your other point, oxide colors. Before trying the D2 steel, I did a few blades from old wood rasps and W2 steel. The only color I saw after the canola oil quench was black scale. It wasn't until I decided to try D2 and got a lot of great information from guys here on that process that I've actually seen color on the blade after the plate quench. And now, after heat treating 4 D2 blades, I've not seen the same "color" on them.
The first one came out black with a light coating similar to powder coating. This I meticulously sanded off to get a bright shiny blade. I think I didn't get the foil sealed well enough.
The 2nd one came out with really nice red, blue, yellow and green swirls on it, but mostly red color.
The 3rd one had the same colors, but not to the same extent, there was one area about 1x1.5 inches with almost no color.
The 4th one again came out with the black "powder coat", but it was the one that also warped. After sanding the coating off, I did the steps to remove the warp (twice) and it is a real nice solid gun metal blue color.
Is there a write-up somewhere on how to interpret these colors?

I'm thinking I would be better off spending the $$$$ to get better controls for my kiln. Problem is, they want more for the digital controls than I paid for the kiln! (I bought it used at an estate sale.)

I think what Mr. Robinson was talking about is most hand testers don't get closer than +-2 HRC and are usually set for thicker parts. As for those scratch testers they are in increments of 5 points. The Rockwell scale is like the Richter scale, in other words it's exponential. I couldn't live with a 5 point chance of being off. RC 56 is a LOT softer than RC 58! RC 60 is also a lot harder than 58. I can determine hardness with my diamond hone by feel better than that.

It is a non-linear measurement and I haven't found a study that gives precise numbers to the difference between 58 and 59, like is it 40% harder or is it 4x harder? I've seen some makers say that it's 10x because it scaled in decimal points like 59.7, but I haven't been able to find a scientific study that gives that precise value. Suffice to say that the 10x maybe very close. If anyone knows a study that does give the values I would like a link to it.

Now after confusing myself and probably you too Al about the hardness factors, I could add the RC 60 with D2 is going to be different with CPM 154 at 60. I prefer D2 as the Vanadium makes it more wear resistant. But 154 is tougher. Different steels mean different trade offs.

I did make my own tester files when I worked at my last job and they go from 55 to 61.2 in different increments that are not exactly even. Like I go from 57. 3 to 58 to 58.9 to 60, but they work, I don't make a knife under 58, nor will I buy one less than that with some exceptions. A 1080 fighter I will leave softer as edge holding isn't as important as toughness and flexibility. In other words, you don't want it to break if you've been attacked by a bear.

Oxide colors get a bit weird on stainless steel, since, you know, they aren't supposed to oxidize. I really only use the oxide colors as a backup method to make sure I had the right tempering temperature, a well calibrated method of heat control is really all you need.

Back to the hardness files, jimm does bring up the very solid fact that they do jump in increments of 5, so the results won't be quite as accurate. As I already said thoughts, my personal opinion is that knowing the exact rhc is unnecessary, and ballpark (within a few points) is good enough. I also believe that files are a perfectly serviceable way of getting inside the ballpark, when combines with the data sheet for whatever steel I'm working with.

In my case, I work primarily with 1095. I know that 1095, properly heated and quenched in appropriate quenchant, will reach a Max hardness of about 65rhc, which is about as hard as steel gets. I also know thats more than hard enough to prevent your average metal file (typically 61-63rhc if memory serves) from biting in. According to the data sheets, tempering full-hard 1095 at 450 should bring the hardness down to about 60-61rhc, and at that point a file should just barely bite into the steel. Bring the tempering temperature up and the hardness down to the 57-58 range, and you can feel the change in how the file bites into the steel. Its subtle, but there enough to notice.

Is it perfect and accurate to withing a point? No, not at all, if you need within a point of accuracy you should probably invest in one of those $1000 hardness testers. It is, however, accurate enough for my needs

Jim,
Wow, I wsn't aware that the Rockwell scale was exponential, that's a huge difference! Having majored in math and minored in physics in college I am well aware of the significant difference.
In many exponential scales, 1 point means 10x harder. So, a reading of 60 would be 20x harder than 58. I agree, it certainly would be nice to have a printed scale on this. A 50x hardness difference would be huge. However, it might require a different scale for different formulas of steel.

With the blades I just treated, my diamond files will bite into the metal, but not nearly as hard as before heat treating, my regular files just slide across without doing anything.

So Guys, I guess the moral of the story is that if you don't want to fork out big bucks or don't really need precise accuracy, than a expensive tester isn't necessary, BUT it then becomes necessary to precisely follow the heat treating instructions for the steel you are using and the purpose of the item you are making.

I may do some research into finding out if there are any scientific info on this.

Yes Al, it's even more confusing when you read some of the actual scientific literature where it talks about non-Archimedes linear scale values (HUH?), but the difference is quite detectable when you get up to RC 58 and higher as I can sharpen a knife at 58 with regular stones in a decent amount of time, but RC 59 and 60 I need the diamond or it just takes too long. I think I said I think your knives are probably close to RC 61 according to your temper temperature.

Following directions when I had access to a tester was really quite close to what I needed for knives though most directions I had were for machine parts. D2 though was always for blades and those for cutting paper, thickness ran from 3/8 to 3/16" and lengths varied. I had the advice of a HT company I had to send the longer blades to.

Guys like SamaraiStuart taught me about O1 HT and some things not in the "book". So study everything you can and this is a good place to learn new ideas.

That term sounds vaguely familiar . . . . . . something from about 40 years ago! Too many cobwebs around it to put it into any context!

Know what you mean. I have a couple Western knives, they are nice knives, but don't hold an edge like a Buck knife I have. I could get a very sharp edge on the Westerns with standard sharpening stones in a few minutes, but it took forever to get a good edge on the Buck. This was before I got my diamond hones. Back then, Buck knives were known for being pretty tough, but I heard of several snapping when subjected to hard use.

I tested the edge on my second blade after working on it for a little over half an hour with my 600 grit diamond hone, it cut through 2 feet of cardboard like a hot knife through butter. I am going to do the "brass rod" test tomorrow.

The bar stock I started out with is 5/32nd inch, so after grinding the sides flat, it is right around 1/8th inch thick when I start the primary bevel.

Agree with you, after being a member here for about three years I have learned a lot from some very smart people! It was from discussions I read here that convinced me to try the D2 steel. It is difficult steel to work, but the results are turning out just what I was looking for. I tried W2, but didn't like the results. The couple knives I made out of old wood rasps turned out very well, (due in large part to info from guys here) but quality old rasps and files are getting difficult to find. The advice to get bar stock from NJSB also came for here, and they are great people.
I will continue visiting this site for as long as possible!